//! Streaming, cancellation, size-bound, and timeout semantics of the HTTP
//! engine against a real loopback socket (`SMH-SPEC-SPEC0001`, network transport).

use smith::http::{
    HttpBodyEnd, HttpBodyItem, HttpExchange, HttpExecutor, HttpMethod, HttpResponse,
};
use smith::tool::CancelHandle;
use smith_harness::http::{MAX_BODY_BYTES, UreqHttpExecutor};
use std::io::{Read, Write};
use std::net::{TcpListener, TcpStream};
use std::sync::mpsc::{self, Receiver, RecvTimeoutError, SyncSender};
use std::time::{Duration, Instant};

const EVENTS: [&str; 3] = ["data: one\n\n", "data: two\n\n", "data: three\n\n"];

/// Upper bound on any single wait for the fixture or the engine.
const DEADLINE: Duration = Duration::from_secs(10);

/// Accept one connection, read the request head, hand the socket to
/// `serve`, then drain until the client closes so unread request bytes
/// never turn the close into a reset that discards in-flight response data.
fn spawn_server(serve: impl FnOnce(&mut TcpStream) + Send + 'static) -> u16 {
    let listener = TcpListener::bind("127.0.0.1:0").unwrap();
    let port = listener.local_addr().unwrap().port();
    std::thread::spawn(move || {
        let (mut socket, _) = listener.accept().unwrap();
        let mut buffer = [0u8; 8192];
        let _ = socket.read(&mut buffer);
        serve(&mut socket);
        let _ = socket.shutdown(std::net::Shutdown::Write);
        let _ = std::io::copy(&mut socket, &mut std::io::sink());
    });
    port
}

/// Chunked SSE: head plus first event at once; each later event only once
/// the test sends on the returned gate, so the client must stream what it has.
fn serve_events() -> (SyncSender<()>, impl FnOnce(&mut TcpStream) + Send + 'static) {
    let (gate, next) = mpsc::sync_channel::<()>(EVENTS.len());
    let serve = move |socket: &mut TcpStream| {
        let head = "HTTP/1.1 200 OK\r\nContent-Type: text/event-stream\r\n\
                    Transfer-Encoding: chunked\r\nConnection: close\r\n\r\n";
        let _ = socket.write_all(head.as_bytes());
        for (index, event) in EVENTS.iter().enumerate() {
            // synchronize: the test releases each later event.
            if index > 0 && next.recv_timeout(DEADLINE).is_err() {
                return;
            }
            let _ = write!(socket, "{:x}\r\n{event}\r\n", event.len());
            let _ = socket.flush();
        }
        let _ = socket.write_all(b"0\r\n\r\n");
    };
    (gate, serve)
}

/// Hold a fixture until the test is done with it, bounded by `DEADLINE`.
fn stall(release: &Receiver<()>) {
    // synchronize: the stall lasts until the test releases it.
    let _ = release.recv_timeout(DEADLINE);
}

/// The next body item, or a failure once `DEADLINE` passes.
fn next_item(response: &HttpResponse) -> HttpBodyItem {
    let item = response.body.recv_timeout(DEADLINE);
    assert!(item.is_ok(), "body stalled: {item:?}");
    item.unwrap()
}

fn chunk(event: &str) -> HttpBodyItem {
    HttpBodyItem::Chunk(smith::http::HttpChunk {
        bytes: event.as_bytes().to_vec(),
    })
}

/// Every chunk, then how the body ended.
fn drain(response: HttpResponse) -> (Vec<Vec<u8>>, Option<HttpBodyEnd>) {
    let mut chunks = Vec::new();
    for item in response.body {
        match item {
            HttpBodyItem::Chunk(chunk) => chunks.push(chunk.bytes),
            HttpBodyItem::End(end) => return (chunks, Some(end)),
        }
    }
    (chunks, None)
}

fn post(executor: &dyn HttpExecutor, port: u16, cancel: CancelHandle) -> HttpResponse {
    let exchange = HttpExchange {
        method: HttpMethod::Post,
        url: format!("http://127.0.0.1:{port}/v1/chat/completions"),
        headers: Vec::new(),
        body: b"{}".to_vec(),
    };
    executor.execute(exchange, cancel).unwrap()
}

#[test]
fn chunks_arrive_incrementally() {
    let executor = UreqHttpExecutor::new();
    let (gate, serve) = serve_events();
    let port = spawn_server(serve);
    let response = post(&executor, port, CancelHandle::new());
    assert_eq!(response.head.status, 200);
    // Each event arrives before the server may send the next: a buffering
    // client would stall here instead.
    for (index, event) in EVENTS.iter().enumerate() {
        if index > 0 {
            gate.send(()).unwrap();
        }
        assert_eq!(next_item(&response), chunk(event));
    }
    assert_eq!(
        next_item(&response),
        HttpBodyItem::End(HttpBodyEnd::Complete)
    );
}

#[test]
fn cancel_after_first_chunk_stops_the_reader() {
    let executor = UreqHttpExecutor::new();
    let (gate, serve) = serve_events();
    let port = spawn_server(serve);
    let cancel = CancelHandle::new();
    let response = post(&executor, port, cancel.clone());
    assert_eq!(next_item(&response), chunk(EVENTS[0]));
    cancel.cancel();
    // The reader delivers nothing read after cancellation and ends the body
    // once its in-flight read returns, which the next event forces.
    gate.send(()).unwrap();
    assert_eq!(
        next_item(&response),
        HttpBodyItem::End(HttpBodyEnd::Cancelled)
    );
    assert_eq!(
        response.body.recv_timeout(DEADLINE),
        Err(RecvTimeoutError::Disconnected)
    );
}

#[test]
fn body_over_bound_is_cut_off() {
    let oversized = MAX_BODY_BYTES + 1024 * 1024;
    let executor = UreqHttpExecutor::new();
    let port = spawn_server(move |socket| {
        let head = format!("HTTP/1.1 200 OK\r\nContent-Length: {oversized}\r\n\r\n");
        let _ = socket.write_all(head.as_bytes());
        let block = vec![b'x'; 64 * 1024];
        let mut sent = 0;
        while sent < oversized && socket.write_all(&block).is_ok() {
            sent += block.len() as u64;
        }
    });
    let response = post(&executor, port, CancelHandle::new());
    let (chunks, end) = drain(response);
    let received: u64 = chunks.iter().map(|b| b.len() as u64).sum();
    assert_eq!(
        end,
        Some(HttpBodyEnd::Truncated {
            limit: MAX_BODY_BYTES
        })
    );
    assert!(received <= MAX_BODY_BYTES, "received {received}");
    assert!(received > MAX_BODY_BYTES - 64 * 1024, "received {received}");
}

#[test]
fn ureq_gap_timeout_ends_a_stalled_body() {
    let gap = Duration::from_millis(300);
    let executor = UreqHttpExecutor::with_timeouts(DEADLINE, gap);
    let (release, stalled) = mpsc::sync_channel::<()>(1);
    let port = spawn_server(move |socket| {
        let head = "HTTP/1.1 200 OK\r\nTransfer-Encoding: chunked\r\n\r\n";
        let _ = socket.write_all(head.as_bytes());
        // Keep streaming for longer than `gap` in total, then stall once.
        for _ in 0..3 {
            let _ = socket.write_all(b"2\r\nok\r\n");
            // keep-with-deadline: fixture pacing below `gap`; sleeps last at least this long.
            std::thread::sleep(gap / 3);
        }
        let _ = socket.write_all(b"2\r\nok\r\n");
        stall(&stalled);
        let _ = socket.write_all(b"5\r\nlate!\r\n0\r\n\r\n");
    });
    let start = Instant::now();
    let response = post(&executor, port, CancelHandle::new());
    let (chunks, end) = drain(response);
    let ended = start.elapsed();
    let _ = release.send(());
    let body: Vec<u8> = chunks.into_iter().flatten().collect();
    assert_eq!(body, b"okokokok");
    assert!(
        matches!(end, Some(HttpBodyEnd::Failed { .. })),
        "stalled body ended with {end:?}"
    );
    // keep-with-deadline: time is the contract; the stream outlived `gap`
    // in total, and the stall failed long before its release.
    assert!(ended >= gap * 2, "ended at {ended:?}");
    assert!(ended < DEADLINE / 2, "ended at {ended:?}");
}

#[test]
fn ureq_head_timeout_fails_the_exchange() {
    let head = Duration::from_millis(300);
    let executor = UreqHttpExecutor::with_timeouts(head, DEADLINE);
    let (release, stalled) = mpsc::sync_channel::<()>(1);
    let port = spawn_server(move |_| stall(&stalled));
    let exchange = HttpExchange {
        method: HttpMethod::Post,
        url: format!("http://127.0.0.1:{port}/"),
        headers: Vec::new(),
        body: Vec::new(),
    };
    let start = Instant::now();
    let result = executor.execute(exchange, CancelHandle::new());
    let failed = start.elapsed();
    let _ = release.send(());
    assert!(result.is_err());
    // keep-with-deadline: time is the contract; failed at `head`, long before the stall's release.
    assert!(failed < DEADLINE / 2, "failed at {failed:?}");
}